How can you measure the volume of an object if it is not shaped like a box?
Work out the area of it as if it were 2 dimensional them multiply by the depth.
You can pour water into it. Then check how much the water needed to fill it weights. \(1 dm^{3}\) weights 1 kg.
So if water weight 300 grams, it means that the volume is \(0,3 dm^{3}=300 cm^{3}\)